This application claims the priority of Korean Patent Application No. 2002-40663 filed on 12 Jul. 2002 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a power transmission apparatus, and more particularly, to a power transmission apparatus for a clutchless compressor which can be used for a compressor for a car, lower a starting torque generated at the initial starting and prevent damage to driven apparatuses such as the compressor when the limit torque is generated.
2. Description of the Related Art
Driven apparatuses receiving a rotational force from a driving source such as an engine or other motors of a car use the driving source and a clutch as a power transmission means to transmit power by the connection/disconnection operation of the clutch. In particular, in a compressor used in an air-conditioning apparatus for a car, the power of the engine is usually transmitted by the above operation of the clutch. However, a method of not using the clutch as a power transmission means has been suggested and the method is gradually adopted in the air-conditioning apparatus for a car.
A clutch compressor used for a car does not have a clutch connected/disconnected to a driving pulley by receiving a driving force of the engine, unlike a conventional clutch compressor, and receives the power of the engine so that a rotational shaft of the compressor is always rotated. The clutch compressor is often used for a variable capacity compressor.
The clutchless compressor always receives power via a belt during the driving of a driving motor or an engine. A pulley is rotatably supported on an outer circumferential surface of a nose portion of the compressor via bearings interposed therebetween. The pulley is connected to a pulley of the driving motor via a motorized belt and receives the driving force of the driving motor or the engine. As a hub connected to a driving shaft of the compressor receives a rotational force of the pulley via a power transmission apparatus, the driving shaft of the compressor can rotate.
Since the clutchless compressor always rotates by receiving the rotational force of the engine, when an abnormal torque is generated from the engine, the abnormal torque is transmitted to the compressor as it is, which may damage the compressor.
Thus, in the clutchless power transmission apparatus, when the driving force of a driving source operates abnormally, the abnormal driving force needs to be transmitted to a driven apparatus. Accordingly, methods of disconnection from a driving source in a power transmission apparatus have been suggested.
FIG. 1 illustrates a power transmission apparatus which is disclosed in Japanese Patent Publication No. hei 10-299855. Referring to FIG. 1, a power transmission apparatus 10 includes a connection mechanism consisting of a pulley 11 rotating by receiving a rotational force from an engine, first and second hubs 12 and 13 connected to a rotational shaft of a compressor, an elastic member 14 coupled to connect the pulley 11 and the first and second hubs 12 and 13 and elastically deformable, and first and second support members 15 and 16 supporting the elastic member 14.
In the power transmission apparatus having the above structure, when an over load such as an abnormal torque is applied, the outer circumferential surface of the elastic member 14 slides over the first support member 15 so that the transmission of power is prevented.
In addition to the above invention, many inventions capable of disconnection from a driving source have been developed. However, in the conventional power transmission apparatuses, the structure is complicated and thus manufacturing cost increases. Furthermore, in the power transmission apparatuses, since a mechanism to reduce a starting torque generated at the initial starting is not adopted, fatigue increases so that, after a long-term use thereof, a value of torque at which the transmission of power is disconnected is gradually decreased. As a result, life span of the driven apparatus, in particular, the compressor of an air-conditioning apparatus for a car, is reduced.